The answers would be:
Rift Valley
Mid-Ocean Ridge
New oceanic crust
Here is why:
A divergent boundary is a boundary where two plates are moving apart. (You should remember this so you have an idea about what is formed)
A rift valley is formed when two continental plates (These are plates on land) pull apart, creating a rift in the middle. They are literally ripped apart.
The mid-ocean ridge was formed when oceanic plates moved apart. This also leads use to the new oceanic crust part.
Now when oceanic plates move apart, this leaves space for magma, from beneath the Earth's crust, to occupy and rise. When it goes out through the opening, it is cooled by the water on the surface, so it hardens and becomes new oceanic crust. This goes on and on and this is also how we can explain, seafloor spreading.
*You might be wondering about the Deep Sea Trench. The deep see trench is created by subduction which occurs in convergent boundaries. The trench is the point where the other plate slides under the other. So this is NOT a divergent boundary formation.